1. Field of the Invention
The present invention relates to a vehicle steering system including an upper steering shaft extending downward from a steering wheel provided in a vehicle compartment to pass through an opening in a joint cover mounted on a dashboard, a lower steering shaft extending upward from a steering gear box provided in an engine room, and a joint connecting the upper steering shaft to the lower steering shaft. Also, the present invention relates to such a vehicle steering system in which the steering shaft passes through an opening in the dashboard which separates the engine room containing the steering gear box from the vehicle compartment containing the steering wheel, a grommet is fixed to the steering gear box so as to surround an outer periphery of the steering shaft, and a lip of the grommet abuts against a circumference of the opening in the dashboard.
2. Description of the Related Art
A steering shaft which connects a vehicle steering wheel to a steering gear box passes through an opening in a dashboard which separates an engine room from a vehicle compartment. To prevent engine room noise from entering the vehicle compartment through the opening in the dashboard, a rubber sealing member is fitted in the opening. Japanese Patent Application Laid-open No. 9-242880 discloses a steering system which improves sound insulation performance by superposing two sealing devices each of which comprises a stationary annular portion fixed to an opening in a dashboard, flexible bellows formed integrally on the inner periphery of the opening, and a sealing portion formed integrally on the inner periphery of the flexible bellows and slidably abutting against an outer peripheral surface of a steering shaft.
However, in the conventional steering system, the sealing devices have a complicated structure, resulting in an increased cost. In addition, there are possibilities that sliding noise is generated from a sealing portion of the sealing devices which abuts against the outer peripheral surface of the steering shaft, and steering feeling is deteriorated due to sliding resistance between the sealing portion and the steering shaft.
To avoid such situation, it is conceivable to cause a lip of a cup-shaped grommet mounted on a steering gear box so as to surround the outer periphery of the steering shaft in a non-contact manner, to abut against the circumference of the opening in the dashboard through which the steering shaft passes, thereby preventing engine room noise from entering the vehicle compartment through the opening in the dashboard. However, if such a grommet is used, noise leaking from the steering gear box directly into the grommet enters the vehicle compartment through the opening in the dashboard, resulting in insufficient soundproofing effect.